mu ller



F. MULLER.

MILLING CUTTER.

APPLICATION FILED MAR. 31. 1919.

Patented Aug. 3, 1920.

4 SHEETSSHEET I.

F. MULLER.

' MILLING CUTTER.

APPLICATION FILED MAR. 3|, I9I9.

Patented Aug. 3, 1920.

4 SHEETS-SHEET 2- INVENTOR ATT R EY F. MULLER.

MILLING CUTTER.

APPLICATION FILED MAR. 3h 1919.

1,348,307. Patented Aug. 3, 1920.

4 SHEETS-SHEET 3.

INVENTOR PM M BY 7% T RNEY F. MULLER.

MILLING CUTTER;

APPLICATION FILED MAR. 31.1919.

1,348,307, Patented Aug 3,1920.

4 SHEEI S-SHEET 4- TT RNEY lJNlTED STATES FRIEDTERIOH Mll'LLElt, F HARTFORD, CONNECTICUT, ASSIGNOR TO PRATT & WHITNEY A CORPORATION OFNEW JERSEY.

CO1VIPALNY, 0F NEl/V YORK, N. Y.

PATENT oFFicE.

' MILLING-CUTTER.

' Specification of Letters Patent.

Patented Aug. 33, 1%.30.

Application filed March 31 1919. Serial No. 286,521.

To all "whom "it they concern:

' lie it known that l, lliunnniuon lVli'iLLnn, a citizen of the United States, residing at ll artlord, in the county of Hartford and State of Connecticut, have in vented certain new and useful Improvements in lillllll lg- Cutter-sect which the tollowing is a specification.

lt a well known principle in the art of cutting metals that the cutting edge of the tool shouid. preferably be inclined with respect to the rilirection oi? relative movement so as to cll ect a shearing cut. This incllnation is of advantage in that it improves the cutting action and it is also of advantage in that it permits the tool to ei'igagethe worli: gradually and with relatively little shock instead of ei'uigaging it siuldcnly with greater shock. This principle has been applied to relieved milling cutters which are of uniform diameter throughout and has also been applied to milling cutters having a uniform taper from one end to the other. These milling cutters have their cutting edges longitudihally ii'iclined with respect to the axis, the ciiitting edge usually approximately conforming to a helix. Thus each tooth is enabled to engage the work gradually and to effect a shearing cut. 1

l have applied this principle to accurately made and properly relieved formed or contour cutters. .ly a formed or contour cutter 1 mean one in which the diameter varies from end. to end in ways differing from a iiiiiioi'iii taper, the cutter hcing thus adapted to cut a predetermined contour other than a straight line. Prior to my invention it had not been deemed practical or possible to make such cutters with inclined cutting tau-es. The said. invention is presented and claimed in my co ending application for millii'ig cutters, Serial No. 268,344), filed De- (ember 26th, 1918.

The present invention relates to a milling cutter embodying the invei'ition set forth in my said applicatiom Serial No. 268,349, hut having certain additional features oi 1m" proveincnt adapting it for special lends oi? work. The invention, while applicable to milling cutters of various kinds, is especially adapted for a formed cutter in which one or more parts of the contour are sharply inclincd with. respect to the radii so that-the cutting action takes place largely at the side rather than at the periphery. The invention is particularly applicable to a cutter having a convex contour which is symmetrical or approximately so; that is, a contour in which there are two opposite facing cut arising from the inclination of the cutting faces in accordance with my prior invention may be partly offset by the fact that the cutting edges at one side are formed at obtuse angles these cutting edges not only failing to out easily but tending to crowd the cutter bodily toward the other side. One object of the present invention, therefore, is to provide a cutter, aarticularly a cutter such as a gear cutter having a deep contour, which has inclined. cutting faces but which is tree from the disadvantages last above referred to. I attain this object by providing the cutter with cutting faces which are inclined oppositely. Preferably the cutting faces inclined in one direction are arranged alternately with respect to those inclined in the opposite direction.

As to a part of its subject-matter the present application constitutes a continuation of my abandoned application for milling cutters and methods of making. Serial No. 237,705, filed June 1st, 1918. V v y i In the accompanying drawings 1 have shown two different cutters, and 1 have illustrated two forms of method which may be used for making the cutters. It will he understood, however, that the drawings are intended to he merely illustrative and. are not to he construed as defining or limiting the scope of the invention, the accompany ing claims being relied upon for that pur pose. Particularly it will be understood that there can be wide variation in the contour of the cutters, the contours shown be ing merely selected as'typical.

Of the drawings:

Figures 1 and 2 are plan and side views respectively of a milling cutter embodying the invention. A gear cutter has been selected for purposes of illustration.

Fig. 3 is a fragmentary developed sectional view taken along the arcuate line 33 of Fig. 2.

Figs. 4 and 5 are fragmentary diagrammatic plan and side views respectively, on an enlarged scale, of the cutter shown in Figs. 1 and 2. In these views the cutter is shown with a smaller number of teeth, and the angles of inclination of the cutting faces of the teeth are increased, in order to bring out the principles of the invention more clearly.

Figs. 6 and 7 are diagrammatic views illustrating certain features of the cutter shown in Figs. at and 5.

Figs. 8 and 9 are fragmentary diagrammatic views, similar respectively to Figs. at and 5, illustratinga cutter similar to that shown in the said figures but differing therefrom in certain respects.

Figs. 10 andll are diagrammatic views illustrating certain features of the cutter shown in Figs. Sand 9.

Figs. 12 "and 13 are fragmentary side and bottom views respectively of a preliminary milling cutter adapted to be used in making the final cutter shown in Figs. 4 and 5.

Fig. 1a is av diagrammatic view illustrating certain features of the preliminary cutter shown in Figs; 12 and 13'.

Figs. 15 and 16 are fragmentary side and bottom views respectively of another preliminary milling cutter adapted to be used in making the final cutter shown in Figs. 4 and5.

Fig. 17 is adiagrammatic view illustrating certain features of the preliminary cutter shown in Figs. 15 and 16. r

Figs. 18 and 1 9 are fragmentary side and bottom views respectively of a preliminary milling cutter adapted to be used'in making the final-cutter shown in Figs. 8. and 9.

Fig. 20 i a'plan view'of a lathe tool adapted to be used for shaping the preliminary milling cutters.

Fig. 21; is a diagrammatic view illustrating'a method of shaping a preliminary milling cutter, use being made of the lathe tool shown in Fig. 20.' 1

Fig. 22 is a diagrammatic view, illustrat- .ing the preliminary cutter shown in Figs. 12

and 13 in use for milling a tooth of a blank for the final cutter shown in Figs. 4 and 5, the milling operation having been started but not finished. V

F i is a view similar to Fig. 22 but illustrating the toothcompletely milled.

Fig. 24 is a view similar to Fig. 22 illustrating the preliminary cutter shown in Figs. 15 and 16. in use for milling another tooth of the blank for the final cutter shown in Figs. 4 and 5, the milling operation having been started but not finished.

Fig. 25 is a view similar to Fig. 24; but illustrating the tooth completely milled.

Figs. 26 and 27 are diagrammatic views illustrating the preliminary cutter shown in Figs. 18 andltlin use for milling atooth of the blank for the final cutter shown in Figs.

8 and 9.

Figs. 28 and 29 are plan and side views respectively of a single tooth formed by the method step illustrated in Figs. 26 and 27.

Figs. 1 to 5 thereof it will be seen that l have shown a cutter A embodying the invention, a gear cutter having been selected by way of example. A gear cutter with inclined or helicoidal cutting faces not broadly claimed herein, such a cutter being made the subject of my copending application for milling cutters for gears, Serial No. 268,355, filed December 26th, 1918. The cutter A is provided with two sets of generally longitudinal teeth 1 and 2 with grooves 3 and 4: between them. The teeth and grooves are preferably spaced uniformly, or approximately so. The grooves can be of any usual or preferred depth and shape, as required by the spacing and by the depth of the contour. The front walls 5 and 6 of the teeth 1 and 2 respectively constitute cutting faces and these cutting faces are radial or approximately so in order to provide a satisfactory cutting angle. In accordance with the invention, the cutting faces 5 and (3 are inclined or positioned obliquely so that the longitudinal lines of each of them lie at angles to the axis of the cutter. The cutting faces 5 of the teeth I are inclined in one direction and the cut ting faces 6 of the teeth 2 are inclined in the other direction. By preference the teeth 1 and 2 with the respective cutting faces 5 and 6 oppositely inclined are alternated with each other, as clearly shown in the drawings. Preferably the entire grooves 3 and 4; are oblique or inclined the rear wall of each tooth being inclined in the same direction as the front wall of the next following tooth and in the opposite direction from its own front wall. As concerns the broader phases of the invention I do not narrowly limit myself in regard to the nature of the inclination of the front walls or cutting faces but preferably each cutting face conforms to a helicoid. As illustrated each helicoid is one formed by a generatrix following the axis of the cutter and also following a helix on 11 cylinder concentric with the axis thereof the helicoid in this case being radial. The helicoids for the different cutting faces 5 and 6 are oppositely inclined but preferably the degrees of inclination and the longi' tudinal pitches are the same.

The cutter may be made for cutting any desired practica contour. The contour illustrated is that of the space. between two teeth of a spur gear, and the invention is particularly applicable to a cutter, such as a gear cutter, having a contour which is symmetrical or approximately so.

With a cutter such as shown having a deep convex contour, it is obvious that a large part of the cutting will be effected at the sides of the teeth. The cutting angles at the sides of the teeth are therefore lHlportant. Fig. 3 is a developed fragmentary sectional view of the cutter A, the direction of movement during operation being indicated by the arrow. This view shows more clearly the inclination of the grooves 3 and i, and of the cutting faces and 6. It will be seen that a tooth l behind one of the grooves 3 has at one side, in this case the foremost side, an angle 6 which is acute and well adapted for cutting, The same tooth 1 has at the other side, in this case the rearmost side, an angle 7 which is obtuse and not well adapted for cutting. It will therefore be seen that, if all the teeth were the same, one side of the cutter, that is the side having the angles 6, would be much better for cutting than the other side having the angles The 7 side would not only cut poorly but would tend to force the cutter endwise to ward the 6 side. These disadvantages are overcome by the oppositely formed teeth 2 each of which has an angle 6 and an angle 7 on the sides opposite respectively to the angles (2 and the angles f of the teeth 1. As before stated, the respective teeth 1 and 2 are iiireferably alternately arranged. It will be seen that a cutter formed as above described has equal cutting effectiveness at its two sides and that there is no tendency for bodily movement of the cutter laterally. This cutter has all of. the advantages incident to the inclination of the cutting faces, and in addition each of the teeth has at one side a cutting edge which is especially effec tive-because of the acute angle thereof.

It will be noted that the foregoing discussion to the angles 6 and f is wholly applicaliile only to a cutter having a convex contour. For a cutter having a concave contour the acute-angled side of each. tooth is to the rear of the obtuse-angled side instead of in advance thereof, and the invention is therefore less advantageous as applied to such a cutter.

The outer edge of each cutting face has an outline which is shaped to out either all or at least a. part of the predetermined contour when the cutter is rotated, this outline of the cutting face following the helicoidal surface thereof. Each cutting face 5 or 6 of the cutter A has an outline such that each tooth will cut the entire predetermined contour, as shown by full lines in Figs. 6 and 7. This outline includes the points 21, 22, 28, 24 and All points along the outline are at their respective correct distances from the inward from the outline of the cutting face,

these relief lines forming a continuous surface or continuous surfaces which extend from end to end of the cutter and which are properly constructed notwithstanding the variations in radius at different points :1:

along the said outline and notwithstanding the variations in angular position resulting "from the warped or helicoidal cutting face.

Preferaliily the. relief lines 7 or 8 of each tooth are maintained in similar relationship to each other as they extend backward and inward, the lines preferably conforming to spirals of Archimedes. 7

As the result of the spiral relief each tooth 1, at any axial plane of intersection,

such as 6-6, he. a distorted shape, as shown by dotted lines in Fig. 6. This distorted shape includes points 81, 32, 33, 34; and 85 corresponding respect1vely to the points 21,

22, 23, 24 and 25 on the outline of the -uti ting face The distortion of shape results from the fact that the successive inward inclined relief lines 7 start at different an- .gular positions because of the inclined or Therefore with the i:-

helicoidal cutting face. cutting face 5 inclined in the direction shown the several points 84, 33, 32 and 31 to the left of the point 25 or are spaced inward from the respective points 24:, 23, 22 and 21 by progressively increasing distances. llotwithstanding this distortion in shape at an axial plane of intersection, the outline or effective contour at the cutting face 5 is correct, as before stated. Similarly each tooth 2, at axial plane of intersection, such as 7-7, has a distorted shape as shown by dotted lines in Fig. 7. This distorted shape includes points 4:1, 42, 43, 4A: and 45 corresponding respectively to the points 2i, 22, 23, 24- and 25 on the outline of the cutting. face 6. With the cutting face 6 inclined in the direction shown the several points 42, a3, i l and to to the right of the point 21 or 41 are spaced inward from the respective points 22, 23, 2a and 25 by progressively increasing distances. Notwithstanding this distortion in shape at an axial plane of intersection, the outline or effective contour at the cutting face 6 is correct, as before stated' Inasmuch as all of the teeth have an effective contour, which is the same as the predetermined contour, the cutter will cut the said predetermined contour when used.

l/Vhen. the relief lines 7 and 8 conform to spirals and are maintained in similar relationship as they extend backward and inward, as is preferred, it is possible to sharpen or grind the teeth of the cutter on the front cutting faces and 6 without changing the effective contour. The teeth present the same eifectivecontour at successive inclined surfaces of intersection similar in form and position to the initial cutting faces. At any surface, such as g-g, back of the initial cutting face of a tooth 1. and similar tothe said face, the same effective contour will be foruid. Similarly at any surface, such as L/i back of the initial cutting face 6 of a tooth 2 and similar to the said face, the same effective contour will be found. l herefore ifthe cutter is ground on the front faces to helicoids which are the same as the helicoids of the initial cutting faces t 1e effective contour will remain the same.

it is obvious that with a cutter constructed. as, shown aud'described each tooth will be most effective for cutting at its acute-angled side, in this case the front or foremost side. The rear obtuse-an 'led side will be relatively ineffective for cutting. In order tl at the obtuse-angled sides may not interfere with the cutting action and re duce the efficiency thereof, it is sometimes preferable to provide a cutter such as B shown inFi-gs. 8 and 9 having teeth 9 and 10 which are so shaped that each of them is capable of cutting only at the acute-angled side, the obtuse-angled side being reduced so as to provide a clearance.

The teeth 9 and 10 of the cutter B are separated by grooves 11 and 12. and the teeth are provided respectively with cutting faces 13 and I4 similar respectively to the faces 5 and 6 of the cutter A. The teeth are relieved respectively along spiral lines 15 and 16. The cutter B is ormay be simila to the cutter A except as hereinafter described. As shown by full lines in Fig. 10, the cutting. i

p 00 13 of each tooth 9 has at its left acute-angled or foremost side an outline 21, 22, 23 such that the tooth will cut at least the left half of the predetermined contour'21, 22, 23, 2,1, 25. The right obtuseangled or rearmost side has an outline which is slightly reduced below the desired contour, the amount of reduction gradually increasing from the center toward the right. The reduced outlineat the right is indicated by23, 24- 25. As shown by full lines in Fig. 11 the cutting face 14 of each tooth 10 has at its right acute-angled or foremost side an outline 23, 24, 25 such that the tooth will cut at least the right half of the predetermined contour 21, 22, 28, 2 1, 25. The left obtuse-angled or rearmost side has an outline which is slightly reduced below the de sired contour, the amount of reduction gradually increasing from the center toward the left. The reduced outline at the lef t is indicated by 23, 22, 21.

Each tooth 9 at any axial plane of intersection, such as 10-10, has a distorted shape 31, 32, 33, 3st and as shown by dotted lines in Fig. 10. The shape 'll. 32, 3 at the left is the same as the left half of the shape 31, 32, 33, 34-, 35 of a teeth 1 of the cutter A as shown in Fig. (3, but the shape 33, 31-", 315 at the right is reduced below the said shape 31, 32, 33, 3 1-, 35, the amount of reduction gradually increasing from the center toward the right. Each tooth 10 at any axial plane of intersection. such as .1ll 1, has a distorted shape .11 -12, 43, 4-4 and 15, as shown by dotted lines in Fig. 11. The shape -13. ll 15 at the right is the same as the right hal i' of the shape 21, 22, 23, 21, 25 of atooth E3 of the cutter A as shown in Fig. 7, but the shape 41:3, 42 and 41 at the lcft is icduccd below the said shape 4:1, 42, 113, 4:1, 15, the amount of reduction gradually increasing from the center toward the left. Inasmuch as each alternate tooth has an effective coutour which is the same as one-half of the predetermined contour and each other tooth has an effective contour whicu is the same as the other half of the predetermined contour, the cutter has a composite contour which is the same as the predetermined contour and it will. cut the said contour when used. The cutter l), like the cutter A, can be sharpened or ground on the front cutting faces 13 and 1 .1: without changing the effective contour.

To assist in giving a more complete understanding of my invention, I will set forth a. method by which my improved milling cut ters may be made. I will first describe a form of the method which is adapted for the making of the cutter A and I will then describe a form of the method which is adapted for the making of the cutter I). it will be understood that with either form of the method the preliminary steps of turning the blank, cutting the grooves therein. etc, can be carried on in any usual or preferred way, these steps not rmpiiring any special description. The u'icthods are prcsented and claimedv in my copcnzluur applications for methods of making milling cutters, Serial Nos. 286.522 and 286.523. filed on even date herewith. I will here n confine myself to a. brief description of simple forms of the said methods. reference being made to the said applications for more detailed descriptions.

In practising the method there is provided a preliminary cutting means which may be either one or two preliminary cutters adapted to be used to form the shape of the final milling cutter. Preferably the preliminary cutters are milling cutters and they will be. so described. For making the cutter use is made of two milling cutters R and S, shown respectively in Figs. 12'to 14 and 15 to 17. For making the cutter B use is preferably made of a single milling cutter T shown in Figs. 18 and 19.

The cutter ll is provided with generally longitiuilinal teeth 46 which are separated by grooves 47 and which have front cutting faces 48. Each tooth of the preliminary cutter It has at any axial plane of intersection such as 14-14 ashape which is the same or approximately the same as the predetermined contour, as shown by dotted lines in Fig. 14. While the contour is the same, it is reversely positioned with respect to the axis, the points which are outermost on the final cutter being innermost on the preliminary cutter and vice versa. The points along this plane of intersection are indicated by 21 22, 2t- 24 and 25 these corresponding respectively to the points 21, 22, 2-3, 24 and 25 on the effective contour of the final cutter A.

The front cutting faces 48 of the teeth 46 of the cutter R are helicoidal in form and have the same longitudinal pitch or lead as the helicoidal faces 5 of the teeth 1 of the cutter A. The cutting faces 48 and the cutting faces 5 are inclined in the same direction. The preliminary cutter R is preferably much smaller in diameter than the final cutter, and therefore there is an apparent difference in the helicoidal. surfaces of the two cutters. While the helicoids are in reality the same, being determined by the same or similar directrices, the actual angle of inclination is for the preliminary rutter Pt than for the final cutter A. because oil. the smaller diameter. The actual angle of inclination of the cutting faces of the preliminary cutter is immaterial. and therefore the diameter of the preliminary cutter R can be varied as desired without interfering with the practise of the method. For the cutter it as illustrated in Figs. 6 and 7 the length 11 of the cutter may be taken as the unit of length, and it will be seen that the corre sponding angular advance is represented by j. For the cutter R as illustrated in Figs. .12 and 13 the same unit of length 2' is taken, and the angular advance j is kept the same.

Each tooth 46 of the preliminary cutter ll has a degree of relief which is tl e same as the degree of relief of the teeth of the final cutter. The degree of relief in each case is represented by the ratio between the angular advance of the cutter and the decrease in diameter. The decrease in diameter for each angular increment of advance of the cutter It is the same as the decrease in diameter for each angular increment, of advance of the cutter A. While the degrees of relief are the same for both cutters, there is an apparent difference because of the smaller diameter of the cutter ll. This causes the relief lines to meet the circumferentiallines at a relatively small angle such as for the cut ter A and at a relatively large angle such as 7.7" for the cutter R, but it will be remembered that the degrees of relief are the same, as before explained.

As the result of providing the teeth of the preliminary cutter R with the same helicoidal cutting faces and with the same degree of relief as the teeth 1 of the final cutter A, the front outline or effective contour of each tooth is distorted, as shown by full lines in Fig. 14. The points 31 32 33 34" and 35 along the distorted outline correspond respectively to the points 21 22*, 23 24" and 25" along the shape at an axial plane of intersection. The several points 34", 33 32" and 31" to the right of the point 25 or 35*" are spaced outward from the respective points 34" 33*, 32 and 31 by progressively increasing distances. The actual inclination of each cutting face is less by reason of the smaller diameter but the amount of relief is more for the same reason, and these differences exactly compensate for each other. The result is that the distortion of the outlines 31", 32 33 34*", 35 of the teeth of the cutter R is exactly the reverse of the desired distortion 31, 32, 33, 34, 35 of the teeth 1 of the final cutter A along axial planes of intersection, the two distortions being exactly the same in extent.

The cutter S has teeth 49 with grooves 50 between them, the teeth being provided with helicoidal cutting faces 51. The cutter S is exactly like the cutter R except that the cutting faces 51 are inclined in the direction opposite to that of the cutting faces 48. Each tooth of the preliminary cutter S has at any axial plane of intersection such as 17-17 a shape which is the same or approximately the same as the predetermined contour, as shown by dotted lines in Fig. 17, and also the same as the shape 21 22, 23 24 25" of the tooth of the cutter R. The points along this plane are indicated by 21 22 23 24 and 25 The distorted front outline or effective contour of each tooth is 41 42 43 44 and 45 the several points 44 43 42 and 41 to the left of the point 25 or 45 being spaced outward from the respective points 24 23 22 and 21 by progressively increasing distances. The distortion of the outlines 41 42 43 44 45 of the teeth of the cutter S is exactly the reverse of the desired distortion 41, 42, 43, 44, 45 of the teeth 2 of the final cutter A along axial planes of intersection, the two distortions being eX- actly the same in extent.

The cutter T has differing teeth 46 and 49 with grooves 52 and 53 between them, the teeth being provided respectively with helicoidal cutting faces 48 and 51. Each tooth 46 is similar to a tooth 46 of the cutter R, and each tooth 49 is similar to a tooth 49 of the cutter S. Each tooth 46 has a distorted front outline or effective contour 3P,

' 32, 33, 34rand 35 which is thesame as the contour31", 32 33", 3 1", of the cutter B. Each tooth 49 has a distorted front outline or effective contour 4P, 42 an, 44 and &5 which is the same as the contour L1 e2 3 44?, of the cutter S.

Any of the-preliminary cutters R, S or T can most conveniently be made by means of a lathe tool such as V, shown in Figs. 20 and 21, this tool being used in a relieving lathe. The lathe tool V is formed with a contour 21", 22?, 23 24; and 25 on its top cutting face which is the same as the effective contour of the teeth of' the final cutter A. Fig. 21 shows the cutter B being formed, it being understood that it is rotated in the direction of the arrow and that the tool V is moved in and out, as indicated by the horizontal arrow, so as to follow the proper relief. The operation .i's-exactly the same for the cutter S or the cutter T. In the case of each cutter all of the teeth can be made in the one operation as they have the same cross-sectional shape. In order to make a small correction, it is sometimes desirable to set the tool V with the top cutting face in a plane at an angle to a plane throughthe axis of the pre liminary cutter, as indicated in Fig. 21.

' This small correction is necessary by reason of the angle that is formed between the spiral relief-lines and the radial cutting faces. The nature of the'correction and the manner of making it. are fully set forth in my copending application for method of making milling cutters Serial No. 268,350, filed December 26, 19.18.

In making the cutter A both of the cutters R- and S are used, as shown in Figs. 22 to 25. Either cutter may be used first and I will first describe the use of the cutter R.

Figs. 22 and 23 show the preliminary cutter R- in use formillingthe teeth 1 of the 'final cutter A. It will be understood that the cutter R is rapidly rotating in the direction indicated by the arrow thereon; that the blankA is slowly rotating in the direction indicated by the arrow thereon; and that relative approaching and receding move ments are eflectedbetween the cutter and the blankin timed relation to the blank rotation to @providethe required relief on the final cutter. T'hese relieving movements are preferably effected moving the axis of the cutter bodily toward the axis of the blank. as indicatedby the vertical arrow, and then bodily awayfrom the axis of the blank in the opposite direction. Preferably the downward or inward relieving movement is so timed that the resulting relief on the blank will conform to spirals of Archimedes. The cutter R is moved slowly downward during the cutting ofeach tooth 1 and then is rapidly moved upward between he teeth to position it for the cutting of the next tooth 1. The timing of the relieving movements is such that the teeth 2 are not ongaged.

As shown in Fig. 22, the cutter 1t and the blank A have been so adjusted that the teeth 4:6 of the rotating cutter D will mill the initial point Ll of the tooth 1 of the blank A to the required distance from the axis. The dowmvard IllOVClIlOllt of the cutter R in timed relation to the slow rotation of the blank A causes it to take a cut which graduallyincreases in depth at the successive points 23. Q-land 25 back of the point 21. This action is continued till the relative position shown in F 23 is reached. In this milling action the dis torted shape of the cutter R causes the de sired distortion in the shape of the teeth 1 of the cutter A. The cutter R shapcs the teeth 1 with the several points 21, Q2. 2 2st and 25 all at the proper distances from the axis, so that these teeth when used will cut the true predetermined contour. as shown by full lines in Fig. 6.

The action of the cutter 5 as shown in Figs. 2-1; and 25 is exactly the same as that of the cutter 1?. except that the teeth J are engaged instead of the teeth '1. The distorted shape of the cutter t causes the dcsircd distortion in the shape ot the teeth 52 of the cutter A. The cutter S shapes the teeth 2 with the several points BL i2. 2i 2% and 25' all at the proper distances from the axis so that these teeth when used will cut the true predetermined contour. as shown by full lines in Fig. 7.

In making the cutter B both cutters l? and may be used, the operation being the same as that shown in Figs. 22 to 2?. except that each preliminary cutter engages each tooth of the final cutter. Preferably. however. the cutter T is used. as shown in Figs. 26 to 33. The cutter T is shown in Fig. 2G with one of its teeth 4(3 engaging: a tooth 9 of a cutter blank it For the present let it be imagined that the cutter T has only the teeth 4-6. the teeth l5) being omitted. The cutter T is assmned to be rotating rapidly. as indicatwl. and the blank 13 is assumed to be rotatin; slowly in the opposite direction. as indicated. It is also assumed that relatn approaching and receding movements are etTccted between the cutter and the blank in timed relation to the blank rotation to provide the required relief on the finished tooth. The action of the teeth 4-6 of the cutter T taken by th nr selves, is exactly the same as that of the cutter R. as shown in Figs. 22 and 2d. Tin teeth do would mill the tooth 9 to the form shown, this tooth in transverse sec tion having a distorted shape as iud..rted by dotted lines in Fig. (3. but n( \c1 i;'lcspresenting an effective contour if.

ill)

24, 2!) at the cutting face which .is correct for cutting the predetermined contour.

Fig. 27 is a view similarto Fig. 26 but showing the cutter T with one of its teeth 49 engaging a tooth to of the cutter blank B. in considering this figure let it be imagined that the cutter T has only teeth 41th, the teeth to being omitted. The teeth ll) of the cutter T, if acting by themselves, would mill the tooth to the form shown. Inasmuch. as the cutting faces 51 of the teeth lll are inclined oppositely to the faces 13 of the teeth 9 the teeth 9 are cut with a cross sectional shape which is distorted oppositely to the proper distortion that would be necessary for providing the correct effective contour at the cutting faces. The result is that the teeth 9 have an abnormally distorted contour 21, 22", 23, 24:", at the cutting face,-the part 21", 22", 23 being outside the correct contour 21. 22, 23 as shown in Fig. 6, and the part 23, 24, 25 being inside the correct contour 23, 24:, 25 as shown in Fig. 6. The point 23 of this distorted contour coincides with the point 23 of the correct contour.

Inasmuch as the cutter T actually has both kinds of teeth 4E6 and 49 and inasmuch as these teeth follow each other in rapid succession, the tooth being milled, therefore, never has the entire fo "m 9' shown in Fig.

'26 nor the entire form 9 shown in Fig.

27. The teeth 49 reduce the contour 23, 24-, 25 which the teeth 4:6 tend to cut, and the teeth 46 reduce the contour 21", 22, 23 which the teeth 49 tend to out. As the result of the composite action of the two sets of teeth 4th and t9 the teeth 9 are milled as shown in Figs. 28 and 29. Each tooth has the same contour 21, 22, 23 as the tooth 9 shown in Fig. 26, and has the same contour from 23, 24:", 25 as the tooth 9 shown in Fig. 27. The tooth 9 is effective at its right foremost side to cut the part 21, 22, 23 of the predetermined contour as shown in Fig. 6. The outline 23, 24", 25 of the cutting faceis reduced and will not cut the predetermined contour.

Figs. 30 and 3]. are views similar respectively to Figs. 26 and 27 and illustrate the separate actions of the teeth 49 and 46 in milling one of the teeth 2 of the final cuttor A. The teeth 49 if acting by themselves, would mill the tooth 10 to the form shown, this tooth in transverse section having a distorted shape as indicated by dotted lines in Fig. .7, but nevertheless presenting an effective contour 21, 22, 23, 24, 25 at the cutting face 6, which is correct for cutting the predetermined contour. The teeth 46 if acting by themselves, would mill the tooth 10" to the form shown. Inasmuch as the cutting faces 4L8 of the teeth 46 are inclined oppositely to the faces 14 of the teeth 10, the teeth 10 are cut with a cross sectional shape which is distorted oppositely to the proper distortion that would be necessary for providing the correct effective contour at the cutting faces. The result is that the teeth 10' have an abnormally distorted contour 21 22, 23, 24;", 25" at the cutting face, the part 23, 24 25 being outside the correct contour 23 2e; as shown in Fig. 7 and the part 21 22", 23 being inside the correct contour 21, 22, 23 as shown in 7. The point 23 of this distorted contour coincides with the point 23 of the correct contour. The tooth 10 out by the composite action of the teeth t9 and to is shown in Figs. 32 and Each tooth has the same contour 23, 24, 25 as the tooth 14)" shown in Fig. 30, and has the same contour 21 22 as the tooth 10 shown in Fig. 31. The tooth 1.0 is effective at its left foremost side to cut the part 23, 24:, 25 of the predetermined contour, as shown in Fig. 7. The outline 21", 22 23 of the cutting edge is reduced and will not cut the predetermined contour.

When the cutter B is used, as already stated, the teeth 1. and 2 follow each other in rapid succession, the teeth 1 cutting the part 21, 22, 23 of the contour and the teeth 2 cutting the part 23, 24;, 25 of the contour. Thus the cutter cuts the full predetermined contour, cutting taking place only at the front oblique-angled edges 6, the rear obtuse-angled edges 7' being ineffective.

hat I claim is:

1. A milling cutter for cutting a predetel-mined contour other thana straight line, comprising two sets of generally longitudinal teeth provided respectively with front cutting faces oppositely inclined with re spect to the cutter axis, the said cutting faces having contours adapting them to cut the said predetermined contour and the outer surfaces of the teeth behind the inclined cutting faces being relieved along lines extending backward and inward from the outer edges of the faces to provide an effective contour behind each cutting face which is the same at successive surfaces of intersection inclined similarly to the initial cutting face, whereby the cutter may be ground on the inclined faces without changing the effective contour.

2. A milling cutter for cutting a predetermined contour other than a straight line, comprising two sets of generally longitudinal teeth provided respectively with oppositely inclined helicoidal front cutting faces, the said cutting faces having contours adapting them to cut the said predetermined contour and the outer surfaces of the teeth behind the helicoidal cutting faces being relieved along lines extending backward and inward from the outer edges of the faces.

3. A milling cutter for cutting a predetermined curved contour, comprising two sets of generally longitudinal teeth provided respectively with oppositely inclined helicoidal front cutting faces, the said cutting faces having contours adapting them to cut the saidpredetermined curvedcontour and the outer surfaces of the teeth behind the helicoidal cutting faces being relieved along lines extending backward and inward from the outer edges of the faces.

4:. A milling cutter for cutting a predetermined symmetrical contour other than a straight line, comprising two sets of generally longitudinal teeth provided respectively with oppositely inclined helicoidal front cutting'faees, the said cutting faces having contours adapting them to cut the said predetermined symmetrical contour and the outer surfaces of the teeth behind the inclined cutting faces being relieved along lines extending backward and inward from the outer edges of the faces.

5. A milling cutter for cutting a predetermined concave symmetrical contour other than a straight line, comprising two sets of generally longitudinal teeth provided respectively with oppositely inclined helicoidal front cutting faces, the said cutting faces having convex contours adapting them to cut the said predetermined concave symmetrical contour and the outer surfaces of the teeth behind the inclined cutting faces being relieved along lines extending backward and inward from the outer edges of the faces. V V

'6. A milling cutter for cutting a predetermined contour other than a straight line, comprising two sets of generally longitudinal teeth provided respectively with oppositely inclined helicoidal front cutting faces, the said cutting faces having contours adapting them to cut the said predetermined contour and the outer surfaces of the teeth behind the helicoidal cutting faces being relieved alonglines extending backward and inward from the outer edges of the faces and conforming to spirals constructed about the cutter axis.

7. A milling cutter for cutting a prede te-rminedcontour other than a straight line,

comprising two sets of generally longitudinal teeth provided respectively with oppositely inclined helicoidal front cutting faces, the

said cutting faces having contours adapting them to out the said predetermined contour and the outer surfaces of the teeth behind the helicoidalcutting faces being relieved along lines extending backward and inward from the outer edges of the faces to provide an effective contour behind each cutting face which is the same at successive surfaces of intersection inclined similarly to the initial cutting face, whereby the cutter may be ground on the inclined faces without changing the effective contour.

'8. A milling cutter comprising two sets of generally longitudinal teeth provided re spectively with front cutting faces oppositely inclined with respect to the cutter axis and provided respectively with rear faces each inclined with respect to the axis oppositely from the corresponding front cutting face whereby the major portion of the body of each tooth is directly back of the cutting edge at the acute-angled side.

9. A milling cutter for cutting a predetermined contour other than a straight line. comprising two sets of generally longitudinal teeth provided respectively with front cutting faces oppositely inclined with respect to the cutter axis and provided respectively with rear faces each inclined with respect to the axis oppositely from the corresponding front cutting face whereby the major portion of the body of each tooth is directly back of the cutting edge at the acuteangled side, the said front cutting faces of the teeth having contours adapting them to cut the said predetermined contour and the outer surfaces of the teeth behind the inclined cutting faces being relieved along lines extending backward and inward from the outer edges of the faces.

10. A milling cutter for cutting a predetermined contour other than a straight line, comprising two sets of different generally longitudinal teeth provided respectively with oppositely inclined helicoidal front cutting faces. and provided respectively with rear helicoidal faces each inclined oppositely from the corresponding front cutting face whereby the major portion of the body of each tooth is directly back of the cutting edge at the acute-angled side, the said front cutting faces of the teeth having contours adapting them to cut the said predetermined contour and the outer surfaces of the teeth behind the inclined cutting faces being relieved along lines extending baclnvard and inward from theouter edges of the faces.

11. A milling cutter for cutting a predetermined contour other than a straight line. comprising two sets of generally longitudinal teeth provided respectively with front cutting faces oppositely inclined with respect to the cutter axis, the said cutting faces ha ving contours adapting them to cut the said predetermined contour and alternate faces being reduced at opposite sides respectively below the said predetermined contour. and the outer surfaces of all of the teeth behind the inclined cutting faces being relieved along lines extending baclrinird and inward from the outer edges of the faces to provide an effective contour behind each cutting face which is the same at successive surfaces of intersection inclined similarly to the initial cutting face. whereby the cutter may be ground on the inclined faces without changing the effective contour.

12. A. milling cutter for cutting a predetermined contour other than a straight line, comprising two sets of generally longitudinal teeth provided respectively with oppositely inclined helicoidal front cutting faces, the said cutting faces having contours adapting them to cut the saidpredetermined contour and alternate faces being reduced at opposite sides respectively below the said pre determined contour, and the outer surfaces of the teeth behind the helicoidal cutting faces being relieved along lines extending backward and inward from the outer edges of the faces to provide an effective contour behind each cutting face which is the same at successive surfaces of intersection inclined similarly to the initial cutting face, whereby the cutter may be ground on the inclined faces Without changing the effective contour.

13. A milling cutter for cutting a predetermined relatively deep approximately symmetrical contour, comprising two sets of alternately arranged generally longitudinal teeth provided respectively with oppositely inclined helicoidal front cutting faces, the said cutting faces having contours adapting them to cut the said predetermined symmetrical contour and alternate faces being reduced at opposite sides respectively below the said predetermined contour, and the outer surfaces of the teeth behind the inclined cutting faces being relieved along lines extending backward and inward from the outer edges of the faces to provide an effective contour behind'each cutting face which is the same at successive surfaces of intersection inclined similarly to the initial cutting face, whereby the cutter may be ground on the inclined faces without changing the effective contour.

14. A milling cutter for cutting a predetermined relatively deep approximately symmetrical contour, comprising two sets of alternately arranged generally longitudinal teeth provided respectively with oppositely inclined helicoidal front cutting faces each having acute-angled and obtuse-angled cutting edges, the said cutting faces having contours adapting them to cut the said predetermined symmetrical contour and the faces being reduced at the obtuse-angled edges below the said'predetermined contour, and the outer surfaces of the teeth behind the inclined cutting faces being relieved along lines extending backward and inward from the outer edges of the faces to provide an effective contour behind each cutting face which is the same at successive surfaces of intersection inclined similarly to the initial cutting face, whereby the cutter may be ground on the inclined faces without changing the effective contour.

15. A milling cutter for cutting a predetermined relatively deep approximately symmetrical concave contour, comprising two sets of alternately arranged generally longitudinal teeth provided respectively with oppositely inclined helicoidal front cutting faces each having acute-angled and obtuse-angled cutting edges, the said cutting faces having convex contours adapting them to cut the said predetermined symmetrical concave contour and the faces being reduced at the obtuse-angled edges below the said predetermined contour, and the outer surfaces of the teeth behind the inclined cutting faces being relieved along lines extending backward and inward from the outer edges of the faces to provide an effective contour behind each cutting face which is the same at successive surfaces of intersection inclined similarly to the initial cutting face, whereby the cutter may be ground on the inclined faces without changing the effective contour.

16. A milling cutter for cutting a predetermined relatively deep approximately symmetrical contour, comprising two sets of alternately arranged generally longitudinal teeth provided respectively with oppo sitely inclined helicoidal front cutting faces, the said cutting faces having contours adapting them to cut the said predetermined symmetrical contour and alternate faces being reduced at opposite sides respectively be low the said predetermined contour by amounts gradually increasing from the center to the sides, and the outer surfaces of the teeth behind the inclined cutting faces being relieved along lines extending backward and inward from the outer edges of the faces to provide an effective contour behind each cutting face which is the same at successive surfaces of intersection inclined similarly to the initial cutting face, whereby the cutter may be ground on the inclined faces without changing the effective contour.

17. A milling cutter for cutting a predetermined relatively deep approximately symmetrical contour, comprising two sets of alternately arranged generally longitudinal teeth provided respectively with oppositely inclined helicoidal front cutting faces, the

said cutting faces having contours adapting signature.

FBIEDERICH MULLER. 

